Breast cancer is the most frequent cancer in women worldwide. The highest rate is in North America, with Europe close behind. Most women diagnosed with breast cancer receive radiation to help prevent a relapse, but a new study suggests that such treatment can increase the risk...

Breast cancer is the most frequent cancer in women worldwide. The highest rate is in North America, with Europe close behind. Most women diagnosed with breast cancer receive radiation to help prevent a relapse, but a new study suggests that such treatment can increase the risk of heart attacks and of dying from heart disease up to 20 years later. This increase in risk is particularly pronounced for women with other heart disease risk factors, such as smoking, high BMI or diabetes, at the time of radiotherapy.

It has long been assumed that radiotherapy for breast cancer increases the risk of heart disease later in life. However, little has been known about the nature of the risk, and whether certain individuals are particularly susceptible to ionising radiation. A new study by Swedish, British and Danish researchers sought to address these issues.

The study looked at almost 2,200 Danish and Swedish women who received radiotherapy for breast cancer between 1958 and 2001. Information from radiotherapy charts and medical records were used to estimate mean radiation doses to the heart. Researchers were therefore able to gather information about the medical history and risk factors for heart disease of each woman.

A clear correlation between radiation dose and risk of ischemic heart disease was revealed. The risk was particularly pronounced for women with diabetes, chronic obstructive lung disorders, angina or other heart diseases, a high BMI, or who were smokers at the time of their treatment. The highest risks were noted during the first ten years following treatment, after which the risk decreased, but was still elevated 20 years after radiotherapy.

The risk of a subsequent ischemic heart disease was influenced by age at therapy, previous disorders and heart dose. Comparing a 50 year old breast cancer patient without previous risk factors for heart disease and who had not received radiotherapy, with a woman of similar age with hypertension and high radiation doses to the heart (10 Gy), revealed an approximate three times higher risk of ischemic heart disease in the treated patient.

"The results confirm what we have long suspected, that irradiation increases the risk of myocardial infarction, and that women with other known risk factors for ischemic heart disease are more susceptible than others," says Per Hall, Professor of radiation epidemiology at Karolinska Institutet's Department of Medical Epidemiology and Biostatistics, who coordinated the study. "This gives us stronger grounds on which to weigh the pros of irradiation against the cons of its harmful effects on the heart for individual patients."

Researchers from the following organisations took part in the study: University of Oxford, Royal Surrey County Hospital, and Surrey University, all three in the UK, Odense University Hospital, University of Southern Denmark, Aalborg University Hospital, and Rigshospitalet - Copenhagen University Hospital, in Denmark, University of Southern Florida, US, Karolinska Institutet, and Karolinska University Hospital, Sweden. The study was made possible with funding under the EU's FP6 Radiation Associated Cardiovascular Events (RACE) project. The research team also received grants from the UK Department of Health, the British Heart Foundation, and Cancer Research UK.

The result of the finding were published Wednesday in the New England Journal of Medicine, emphasising the need for better cardiac care for breast cancer survivors, many of whom also take chemotherapy drugs that weaken their heart muscle.